This invention relates generally to a fluid flow control, in which the pressure differential across a variable orifice, positioned between the source of pressure and the load, is maintained constant irrespective of the variation in the system load.
In more particular aspects this invention relates to load compensated valve and pump controls, which control the magnitude of the fluid flow to a fluid motor, subjected to a positive load, by maintaining a constant pressure differential across a control orifice.
In still more particular aspects this invention relates to load compensated valve and pump controls, which permit variation in the level of the controlled pressure differential across an orifice, this pressure differential being maintained constant at each selected level.
Load compensated fluid flow controls are very desirable for a number of reasons. They permit positive load control with reduced power loss and therefore, increase system efficiency. When controlling a positive load they provide the proportional feature of flow control, irrespective of the variation in the magnitude of the load.
Such a fluid flow control, which maintains a constant pressure differential across a variable orifice by throttling the fluid flow delivered to the actuator is shown in my U.S. Pat. No. 3,470,694. A fluid flow control, which maintains a constant pressure differential across a variable orifice, by bypassing part of the fluid flow delivered to the actuator, is shown in U.S. Pat. No. 3,488,953 issued to Haussler. Also such a fluid flow control, which maintains a constant pressure differential across a variable orifice by variation in flow delivery of the system pump is shown in U.S. Pat. No. 3,693,506 issued to McMillan et al.
In all of those patents the variation in flow delivered to a fluid motor is accomplished by a single control input and that is by variation in the area of the control orifice, each specific area corresponding to a specific constant flow level. There are instances where a dual control input in controlling the flow to a fluid motor becomes very desirable.
A system showing a dual control input in control of the flow, namely variation in the area of the control orifice and variation in the level of pressure differential maintained constant across such an orifice is shown in U.S. Pat. No. 4,282,898 issued to Harmon et al. However while the control of Harmon changes the pressure differential acting across a control orifice in response to a control signal, this is accomplished in one step, to a specific higher level, requiring a nonproportional control pressure signal of a magnitude higher than that, equivalent to maximum system load pressure. In Harmon the pressure differential is not proportional to the control pressure signal and cannot be varied in a proportional way with it. Also since Harmon is increasing the pressure differential by compressing a spring, the total range of the pressure signals, equivalent to the preload of the spring, becomes ineffective.